Thanks, also I noticed that for the single-ended OPT's, you did not apply DC current to the primary winding, would that affect the inductance reading compared to when it is used in the actual circuit?
> > How did you measure ep and eR to generate the Zo vs. frequency graph? Just with AC voltmeters?
> I used two-channel AC voltmeter and a floated output AC generator controlled by PC.
> Although differential inputs voltmeter is the best one, I have a voltmeter with common ground input, so upper terminal of a primary winding is grounded and hot terminals of voltmeter are connected to the oscillator to measure eR and eP.